Electrostatographic development method for pressure fixable toners

ABSTRACT

An improved method is provided for fixing pressure-fixable toners of the type having weakly crosslinked amorphous, pressure sensitive polymers wherein the crosslink bonds are disrupted and/or broken by the application of pressure. In the presence of dielectric polar liquids or vapors of polar liquids having insulating (dielectric) properties, the crosslinking forces are substantially reduced and the pressure fixability at ambient temperature is enhanced.

United States Patent [1 1 Erhardt et a].

[ Sept. 2, 1975 ELECTROSTATOGRAPHIC DEVELOPMENT METHOD FOR PRESSURE FIXABLE TONERS [75] Inventors: Peter F. Erhardt, Webster, NY.;

Richard G. Crystal, Dallas, Tex.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Jan. 3, 1974 [21] Appl. No.: 430,438

[52] US. Cl. 427/22; 96/1 SD; 427/23 [51] Int. Cl. GO3G 13/20 [58] Field of Search 117/175, 21; 96/1 R, 1 SD; 355/3 R, 3 DD, 17; lOI/DIG. 13; 118/637,

[56] References Cited UNITED STATES PATENTS 2,976,144 3/1961 Rose 355/3 3,015,304 l/1962 Carlson et a1 117/l7.5

3,132,047 5/1964 VanDorn 118/637 3,199,223 8/1965 Carlson .t 118/637 3,280,036 10/1966 Howell 252/621 P 3,280,741 10/1966 Seymour 252/621 P 3,566,076 2/1971 Fantuzzo et a1. 1 18/637 3,679,302 7/1972 Ludwig 355/17 3,775,326 11/1973 Westdale 252/621 3,788,994 1/1974 Wellman et a1... 252/621 3,804,764 4/1974 Strella et a1 252/621 Primary ExaminerMichael Sofocleous Attorney, Agent, or F irm.1ames .l. Ralabate; Donald C. Kolasch; Ernest F. Chapman 22 Claims, N0 Drawings ELECTROSTATOGRAPHIC DEVELOPMENT METHOD FOR PRESSURE FIXABLE TONERS BACKGROUND OF THE INVENTION The invention relates to electrostatographic image fixing methods, and more particularly, it relates to methods of fixing pressure fixable toners comprising weakly crosslinked pressure sensitive polymers to various substrates.

In the art of xerography, it is usual to form an electrostatic latent image on a suitable insulating or photoconductive insulating surface and to develop this image; thus, making it visible by presenting to the surface an electroscopic marking material. In the usual embodiments of xerography the electrostatic image is formed on a photoconductive insulating surface by charging the surface and exposing it to a' light and shadow image whereupon the charge is dissipated in the light exposed areas. The image is then developed by dusting the image bearing surface with toner or pigment containing materials and this developed image is then transferred to a receiver substrate. It is generally necessary to employ a fixing step in order to cause the image material to adhere permanently to the receiver sheet. Existing fixing operations have generally been limited to fusing the image material by means of heat or solvent-vapor, although other methods such as lacquer spraying, overlaying and the like have occasionally been employed.

In particular, a latent image may be formed on a selenium coated metal surface by applying an electrostatic charge to its surface and exposing the charged surface to a light-and-shadow image whereupon the charge is dissipated in the light exposed areas leaving a latent electrostatic image which can-be developed by cascading electroscopic marking or toner material across the image bearing surface. Alternatively, the toner may be employed for image development by simply blowing it into an air cloud and directing the cloud to the image bearing surface, by mixing the toner with a ferro magnetic material and magneteically conveying the mixture into brushing contact with the image bearing surface, or by dusting the powder material into a brush such as, for example, a fur brush and brushing the image bearing surface.

Upon image development in any of these or other conventional methods, a visible powder image is formed on the image bearing surface. The image may be affixed to the surface by contacting a specially prepared fuser roll system, or it may be transferred to an adjacent receiver surface such as, for example, paper and subsequently affixed to such an adjacent surface.

One conventional method of fixing employs a heating step wherein the toner in image configuration is heated or fused to a paper orother receiving substrate at a temperature below that which would cause damage to the substrate. This technique places limitations upon the design of equipment with regard to short warm-up time, low electric current requirements. adequate heat insulation and uniform heat distribution. Such limitations are particularly critical at high operating speeds. Another conventional fixingmethod employs a vapor which renders the powder image, a tacky, cohesive mass while in the presence of vapor atmosphere. Usually while still tacky it is removed from the vapor atmosphere to air which subsequently leaves the image bonded to the substrate. In general, vapor fixing of powder images denser, blacker images than formed by heat fusing. Particular disadvantages of this process, however, reside in slow drying, solvent retention in paper and other substrates and the release of vapors into the environment.

A class of pressure sensitive toners which can be fixed to a support surface by the application of pressure, has been discovered and disclosed by Strella and Williams in United States Ser. No. 214,441 filed Dec. 30, I971, copending herewith, now U.S. Pat. No. 3,804,764 and incorporated herein by reference. Therein is provided an electrostatographic toner of a finely divided colored resinous material in which the resinous material includes a weakly crosslinked amorphous polymer having a glass transition temperature (Tg) of greater than about 20C. The crosslinks of the polymer, as a result of their weakness, are shear sensitive and can be temporarily disrupted and/or broken by the application of pressure, resulting in a polymer which has the properties of the uncrosslinked polymer. Upon release of the pressure, the polymer reverts to its crosslinked state. Accordingly, such a toner is capable of being fixed to a support medium in image configuration, by the application of pressure. The weakly crosslinked polymer is produced from a polymer having a Tg of less than 40C., with the increase in Tg exhibited by the crosslinked polymer resulting from the production of the crosslinks. Although the pressure sensitive toners are shear sensitive and can be fixed to a support medium by the application of pressure, it is desirable to increase even moreso the shear sensitivity of the toners and thereby enhance pressure flexibility at cold or ambient temperature.

OBJECTS OF THE INVENTION Accordingly, it is an object of this invention to provide a novel method for fixing of the pressure sensitive toner images onto support or receiver material upon which the pressure sensitive toner image is associated.

It is a further object of this invention to provide an improved pressure fixing method for xerographic pressure sensitive toner images.

Another object of this invention is to provide a method which enhances the shear sensitivity of the pressure sensitive toners of the type comprising a weakly crosslinked amorphous, pressure sensitive polymer having a glass transition temperature of greater than about 20C., to enhance pressure fixability at ambient temperature.

Still another object is to provide a method of ambient pressure fixing of the pressure sensitive toners of the type comprising a weakly crosslinked amorphous, pressure sensitive polymer having a glass transition temperature of greater than about -20C.

These and other objects of this invention will become more readily apparent from the following detailed description.

SUMMARY OF THE INVENTION The above objects of the invention are accomplished by exposing the pressure sensitive toner of the type comprising a weakly crosslinked amorphous polymer having a glass transition temperature greater than that 20C. to an agent, more particularly to a dielectric polar liquid, which reduces the forces of associative bonding of the weakly crosslinked amorphous polymer. The agent may be in the form of a vapor or a liquid and may be applied prior to simultaneously with or immediately after the application of pressure. The agent is designated as polar because it encompasses those solvents generally known as polar solvents which are liquids (or vapors) and are capable of developing electrical charges, by ionization, for example, water chloroform, and methanol. Thus, the polar liquids useful in this invention must possess inherent or inducible polarity as well as insulating (dielectric) properties. The agent is also limited to those polar liquids which reduce the forces of associative bonding or ionic attraction of the weakly crosslinked amorphous, pressure sensitive polymers, that is, those which reduce the tendency of the anionic and cationic portions of the weakly crosslinked amorphous, pressure sensitive polymers to interact because of the force of unlike charges within the polymer matrix, said force causing the formation of associative bonds.

The weakly crosslinked amorphous, pressure sensitive polymers and the electroscopic marking materials or toners prepared therefrom are described in United States Ser. No. 214,441 filed Dec. 30, 1971, copending herewith, now US. Pat. No. 3,804,764 and incorporated herein by reference. These polymers are described in more detail infra.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred mode, the weakly crosslinked amorphous, pressure sensitive polymer is exposed to a dielectric polar agent which reduces the forces of associative bonding (ionic attraction) of said weakly crosslinked amorphous polymers, prior to or simultaneously with subjecting the image present on the substrate to pressure, in an electrostatographic imaging method of the type comprising forming an electrostatographic latent image on a surface, developing the latent image with electroscopic marking materials (toners) of the type comprising a weakly crosslinked amorphous, pressure sensitive polymer having a glass transition temperature greater than about C., whereby pressure application to said weakly crosslinked, pressure sensitive polymer results in a polymer having the properties of the uncrosslinked polymer; transferring the developed image to a receiving substrate; and subjecting the image present on the substrate to pressure to fix the electroscopic marking material to the substrate. The process significantly increases the shear sensitivity of the polymer and the pressure fixability at ambient temperature is enhanced. By increase of shear sensitivity is meant the increased tendency of the polymer to deform or shear when subjected to an external force which in the instant case is pressure.

The electrostatographic pressure sensitive polymeric toners used in the process of this invention, are comprised of a weakly crosslinked amorphous polymer the crosslink bonds of which are disrupted and/or broken by the application of pressure whereby the polymer is sufficiently soft to be fixed by pressure, and claimed in United States Ser. No. 214,441 filed Dec. 30, 1971 now US. Pat. No. 3,804,764 as an electrostatographic toner capable of being fixed to a support medium in image configuration by the application of pressure comprising a finely divided colored resin, said resin comprising an amorphous weakly crosslinked polymer having a crosslink bond strength from about 2 to about 30 kcal/mole and a glass transition greater than about 20C., said weakly crosslinked polymer being pressure sensitive, whereby pressure application to said weakly crosslinked polymer results in a polymer having the properties of the uncrosslinked polymer. The process of this invention also applies to encapsulated species wherein the core material comprises the weakly crosslinked pressure sensitive polymer within a shell material, e.g., polystyrene, which is permeable to the passage of the agent.

The weakly crosslinked polymer is produced from a polymer having a Tg of less than 40C., with the increase in Tg exhibited by the crosslinked polymer resulting from the production of the crosslinks. The toners are capable of being fixed to a final copy by the application of pressure.

More particularly, the uncrosslinked polymer (commonly referred to as a prepolymer) from which the weakly crosslinked polymer is prepared is an amorphous polymer which has a Tg from about C. to about 40C., preferably from about -50C. to about 20C. These specified lower Tg limits are only exemplary of the starting materials employed in that polymers with a Tg lower than l00C. can be employed, provided the weakly crosslinked polymer produced therefrom has the specified Tg. The polymer molecular weight (number average) of the uncrosslinked polymer is generally from about 500 to about 100,000, preferably from about 1,000 to about 50,000 and includes more than two crosslink sites per molecule (functionality of molecule is greater than two) which are ,reactable to provide crosslinks having a bond strength from about 2 to about 30 kcal/mole. and preferably bond strengths from about 3 to about 15 kcal/mole. The Tg of the prepolymer and the number of crosslink sites therein are such that, upon crosslinking, the Tg of the crosslinked polymer is raised to a value from about 20C. to about 50C., and preferably to a value from about 20C. to about 50C. Accordingly, the polymer which is used in preparing the toners used in the present invention is a weakly crosslinked amorphous polymer having a crosslink bond strength from about 2 to about 30 kcal/mole, a Tg from about 20C. to about 50C.

In providing the weakly crosslinked amorphous polymers to provide a pressure fixable toner, the molecular weight, crosslink bond strength and glass transition temperature are selected within the specified ranges to provide a polymer having a yield stress sufficiently low to permit yielding by the application of pressure. In general, the weakly crosslinked amorphous polymers which are suitable have a yield stress from about 500 to about 20,000 psi., and preferably a yield stress from about 1,000 to about 5,000 psi.

The weak crosslinks of the polymers are formed by associative bonding (as opposed to covalent bonding), and as representative examples of types of associative bonding there may be mentioned: hydrogen bonding; ionic clustering (sometimes referred to as ionic crosslinking with such weakly crosslinked polymers sometimes being referred to as ionic polymers or ionomers); metal coordinate bonding (including but not limited to chelates); and weak acid-weak base bonding (including but not limited to Lewis Acid Bronsted Base bonding).

The ionic crosslinkages or clusterings are formed, as known in the art, by the polymer including a negative and/or positively charged group(s) either pendant to the polymer backbone, incorporated into the polymer backbone, or terminal to the polymer backbone, which is neutralized by an oppositely charged group to provide the ionic crosslink or cluster.

Although we do not wish to be limited to any theory, it appears that the associative bonds tend to form in localized regions in the weakly crosslinked amorphous, pressure sensitive polymers, for example, styrene/nbutylmethacrylate/potassium methacrylate or n-butylmethacrylate/acrylic acid/potassium acrylate. These may be called clusters or ionic domains, and they tie various macromolecules together within the domain sites. These associative forces are not covalent bonds, but derive their strength from force due to attraction of unlike charges. In the case of ionic clustering, the charges are described by Coulombs law:

where F force of attraction between ionic pairs (1,, charge of the anion charge of the cation 6 dielectric constant of the medium in the region of the ions a separation distance between anion and cation Upon exposure of the polar (or dielectric) agent to the pressure sensitive polymer, diffusion of the agent into the cluster or domain site occurs, causing separation of the associative bonds, e.g., ion pairs so that the distance between ions, a in the expression of Coulombs law, increases, thus decreasing the force of attraction, F. In those cases where the dielectric strength of the polar agent is relatively large, as represented by a relatively high dielectric constant, e.g., greater than 3 at 25C., and the vapor or liquid is thereby somewhat insulating in character, there is a charge shielding effeet which decreases F, the force of coulombic attrac tion expressed in Coulombs law above. As the dielectric constant, e, increases, the force of attraction, F, decreases. The result of either force alone, that is, the charge shielding or the charge separation, or both taken together, is a weakening of, or in the extreme, the breakdown of, the clusters or at least the breakdown of a large number of associative bonds, e.g., ion pairs within the clusters. It is for this reason that the dielectric polar agent or liquid which causes this breakdown is termed a declustering agent. This breakdown results in subsequent ease of separation of the macromolecules when pressure is applied to the pressure sensitive polymer, and it is unique to the weakly crosslinked amorphous, pressure sensitive polymers. The effect of the polar agent or liquid upon the weakly crosslinked amorphous, pressure sensitive polymers enhances the ease of deformation of the polymer when the polymer is subjected to pressure.

Although the weaklycrosslinked amorphous, pressure sensitive toners are capable of being fixed to a suitable support medium, such as paper, to provide a finished copy by the application of pressure, the fixability is significantly enhanced by the process of the present invention. The dielectric polar agent or liquid which significantly enhances the fixability of the pressure sensitive toner at ambient temperatures, is applied simultaneously with the application of pressure, prior to the application of pressure, or immediately after the application of pressure during the time in which residual stresses still remain in the polymer. It may be applied by any manner of application known in the art which will subject the pressure sensitive toner either to vapors of the polar agent or to a fluid layer of the polar agent.

In accordance with the invention, and preferably after development of the electrostatic image with the pressure sensitive toner and its placement in image configuration on a substrate on which it is to be affixed permanently, the pressure sensitive toner is exposed to the dielectric polar agent. However, the exposure step may be carried out prior to the placement of the toner on the substrate on which it is to be affixed or even prior to development of the image, as long as the presence of the solvent at the particular stage of the process does not interfere with the development of the image or the transfer of the toner, e.g., by causing the pressure sensitive toner to become too tacky to develop in image configuration. One skilled in the art can determine at what stage of the electrostatographic imaging, development, transfer (if any) and fixing stage, the dielectric polar agent can be most effectively applied to the pressure sensitive toner to enhance the pressure fixability of the toner.

After the development of the electrostatic image and its placement on a substrate on which it is to be affixed permanently, and either following, or simultaneously with, the exposure of the toner to the dielectric polar agent, pressure may be imparted to the pressure sensitive toner by any suitable means which will affix permanently the pressure sensitive toner to the substrate in image configuration. This may be carried out at cold or ambient temperatures, that is, for example, at the operating temperature of the particular device in which the process of this invention is being used. Even though the process of this invention is particularly suitable for the preparation of a final copy by pressure fixing at cold or ambient temperatures, the process may be carried out in the presence of temperatures above ambient without adversely effecting the process.

The pressure is preferably applied to the pressure sensitive polymeric toner on the substrate by imparting to the substrate bearing the pressure sensitive toner in image configuration, at least 10 pounds per linear inch of pressure. The particular pressure required for affecting such pressure fixing varies with the particular toner or combination of toners employed and the particular dielectric polar agent or liquid applied to the toner, and it can be determined easily by one skilled in the art.

The pressure is preferably provided by pressing the transfer material having the toner image thereon between a pair of polished metal rollers that are in contact with each other under a specified pressure. In general, the roll loading is from about 10 to about 600 pounds per lienar inch, and preferably from about 50 to about 400 pounds per linear inch. The roll loading in pounds per linear inch is the total applied force divided by the length of the roll. In some cases, the pressure fixing of the toner to the support medium may be heat assisted, e.g., by the use of a coated or uncoated heated metal roll and an uncoated or elastomeric coated backup roll.

The pressure is believed to have a twofold purpose. First it embeds the pressure sensitive toner material into the surface of the substrate. Secondly, it permanently affixes the pressure sensitive toner particles which have been exposed to the dielectric polar agent to the substrate bearing the particles. v

The dielectric polar agents which enhance pressure fixability of the weakly crosslinked amorphous, pressure sensitive polymers of the electrostatographic toners, are vapors or liquids which reduce the forces of associative bonding or ionic attraction within the polymer molecule or matrix. The liquids or vapors which may be used to attain the enhanced fixability of the pressure sensitive polymeric toners, must be capable of reaching the sites within the polymer matrix where the associative bonding (ionic attraction) occurs, and accordingly, the pressure sensitive polymeric material must be sufficiently soluble in the dielectric polar agent to permit the liquids or vapors to reach these sites. Thus, there must be at least partial solubility of the pressure sensitive polymer in the polar agent or liquid, and the polar agent is at least a partial solvent for the pressure sensitive polymer.

A quick and satisfactory way to determine if the polar agent provides satisfactory solubility for the pressure sensitive toner is to take a small amount of toner and expose it to the polar agent under consideration for three to five seconds. If the toner becomes tacky or coalesces, the polar agent has generally satisfactory solubility.

When the polar agent is applied as a vapor, the polar agent should preferably have a high vapor pressure.

By high vapor pressure, it is generally meant a boiling point under atmospheric conditions of below about 30C. A heterogeneous multiphase polar agent having a gaseous component which may or may not be a solvent or a polar agent may also be used in the process of this invention. In this case a polar agent having a moderate to moderately low vapor pressure may be used in the process of this invention. By moderate to moderately low vapor pressure, it is generally meant a boiling point under atmospheric conditions of about 100C. or less. It is understood that these vapor pressure values merely guide the selection of a suitable polar agent and/or gaseous component.

The polar agents used in accordance with this invention generally are or have as one component an alcohol, hydrocarbon, aromatic hydrocarbon, halogenated hydrocarbon, halogenated aromatic hydrocarbon, ethers, ketones, esters, acids and the like which meet the above described conditions and which are polar and dielectric in nature in the liquid or vapor form. These materials are applied to the powder image in any convenient manner, but it is preferred to contact the pressure sensitive polymer with vapors or gases containing these materials. While the temperature of application is not critical, it is generally preferred to operate at room temperatures which are generally defined as being between about 65 F. and 80F. Any operable temperature may, however, be selected. Generally any material of the above described class having a boiling point of about 100C. or below may be employed. Typical of such materials are those materials which are selected from the class of noninflammable gaseous and liquid fluorinated hydrocarbons. These are generally available under the trademark freon from the E. l. Du- Pont de Nemours & Company, Inc. Many low boiling fluorinated hydrocarbons when used in conjunction with the pressure step of this invention enhance pressure fixability in accordance with this invention.

Any of the low boiling fluorinated hydrocarbons serve as suitable components when used in conjunction with halogen containing organic materials having boiling points at atmospheric conditions of about 100C. or less. In such mixtures the fluorinated hydrocarbon or other low boiling gaseous or vaporous component is considered to be important to the invention. The low boiling point component is believed to act as a carrier for the higher boiling point polar agent, acting so as to increase the diffusion rates of the polar agent into the polymer e matrix. Inert gases such as, for example, nitrogen or compressed air, have also served as suitable carrier gases for applying the polar agents in the prepressure or pressure application step.

Typical of some of the materials useful in this invention are: benzene, chloroform, carbon tetrachloride, tetrahydrofuran, dichloromethane, fluorotrichloroethane, dichlorodifluoroethane, 1 1 l-trichloroethane, trichloroethylene, l,2-difluorotetrachloroethane, trichlorofluoromethane, chlorotrifluoromethane, bromotrifluoromethane tetrafluoromethane, chlorodifluoromethane, 1 ,2-dichlorotetrafluoroethane, octafluorocyclobutane, fluorodichloromethane trifluoromethane, l 1 -difluoroethane, and l l difluoroethylene. A preferred polar agent used in this invention is dichlorodifluoroemthane.

Typical of mixtures found suitable for this invention include, for example, 50 percent trichloroethylene with 50 percent methylene chloride, 25 percent trichlorotriflouroethane with percent l,l,ltrichloroethane, and 10 percent trichloromonofluoromethane with 40 percent trichlorotrifluoroethane with 50 percent methylene chloride.

It has also been determined that water is a polar agent or solvent which may be used in the process of this invention. Various alcohols, such as, methanol, ethanol, propanol, butanol and the like, alcohols having preferably from about 1 to 5 carbon atoms may be useful in the process of this invention. Acids, such as acetic acid, oxalic acid, chloroacetic acid and the like may also be used as polar agents which reduce the forces of associative bonding of the weakly crosslinked amorphous, pressure sensitive polymers and thereby enhance pressure fixability at ambient temperatures.

It should be understood that the above listings of materials are not in and of themselves all inclusive; any material meeting the cited criteria for this invention are deemed within the scope of this invention.

The vaporizable polar agents may be readily dispersed by any atomizing means employing a carrier or inert carrier such as air, carbon dioxide, nitrogen and the like. The carrier propels the polar agent in the vicinity of the pressure sensitive polymeric toner where it is absorbed into pressure sensitive polymer particle. Upon being taken up by the pressure sensitive polymer particle, there is observed an enhanced pressure fixability at ambient temperature.

The preferred polar agents useful in the process of the present invention are dielectric in nature, that is, they have insulating properties in the liquid or vapor phase. By dielectric or insulative is meant that the liquid or vapor is characterized by low electrical conductivity. Such polar agents would have an electrical conductivity of less than about 10 ohm-cm.

The preferred dielectric polar agent is non-reactive with the pressure sensitive toner and the substrate; it is also non-corrosive with any apparatus materials; and it is non-toxic if released into the surrounding environment.

Recommended amounts of polar agent which can be employed to secure advantageous results can vary from about 0.05 percent to about 0.005 percent by weight of a substrate although amounts less than or greater than the above recommendations can be employed if desired. This value represents the increase in weight of the image bearing substrate such as a film or paper surface carrying the fixed image. The amount of increase depends on the dielectric polar agentabsorbed into the image and substrate. Most of the dielectric polar agents which can be advantageously employed in carrying out the process of the invention are readily available in commerce, and well known.

As can be seen the fixation of the images by this process is quite flexible. For example, an increase in the amount of polar agent used can result in a reduction of the pressure applied to form a fixed image. Polar agents can be applied prior to and simultaneously with the pressure step. These and other modifications of this invention can be made by one skilled in the an and such modifications are included within this invention which is to be limited only by the appended claims. To further demonstrate the invention, the following examples are given which are non-limitative. All parts and percentages are by weight unless otherwise stated.

EXAMPLE I Preparation of Polymer Styrene (10 lb), n-butyl methacrylate (30 lb) and benzoyl peroxide are addedto a mixture of water (80 lb) including tricalcium phosphate'( 1.0 lb) and ALKA- NOL B (7.26 g) as emulsifying agent. The mixture is maintained at 90C. for six hours and cooled to room temperature. 750 ml of concentrated hydrochloric acid is then added to dissolve the tricalcium phosphate. After agitating for minutes, the mixture is washed with water and dried in air.

The styrene-n-butyl methacrylate copolymer has a styrene content of about 35 mole percent, a number average molecular weight of about 44,000 and a Tg of 40C.

The copolymer is dissolved in boiling isopropanol (l2 gal) and potassium hydroxide (4.0 lb) added thereto while maintaining-reflux. After two hours, the mixture is precipitated into a large excess of water and the resulting ionic polymer is washed several timems in water and dried at 90C.

The ionic polymerhas a Tg of 48C. and 5.1 mole percent potassium ions.

Testing of Mechanical Properties Room temperature mechanical properties were determined on cylindrically shaped specimens of the pres sure sensitive polymer prepared above. The specimens were formed by compression molding in a hot press. The specimens were tested in an instrument manufactured by the lnstron Corp. for testing the mechanical properties of polymers by compression while the varying the crosshead speed. The method was an adaptation of the ASTM procedure described for the measurement of compression properties of plastics (ASTM D695-63T, Compressive Properties of Rigid Plastics).

Specimens of the pressure sensitive polymer tested as described above, demonstrated the ductile properties of the pressure sensitive polymer. The pressure sensitive polymer was deformed at crosshead speeds of 0.02

inch per minute and 2.0 inches per minute, demonstrating ductility of the pressure sensitive polymer. However, at a crosshead speed of 20 inches per minute, the polymer underwent brittle failure, that is it failed to form a cohesive ductile mass.

A sample of the pressure sensitive styrene/n-butyl methacrylate/potassium methacrylate polymer prepared above was exposed to saturated water vapor, a dielectric polar agent at room temperature for ten minutes. The pressure sensitive polymer exposed to the water vapor did not undergo brittle failure at a crosshead speed of 20 inches per minute, and the sample was rendered ductile by exposure to the dielectric polar agent, water. This demonstrates the enhancement of the pressure fixability of the polymer.

EXAMPLE 2 Following the procedure of Example 1, the pressure sensitive polymer is sprayed for about three seconds with a vapor of a mixture of 1,1,l-trichloroethane and dichlorodifluoromethane to enhance the fixability of the pressure sensitive polymer to the substrate by altering the ductility of the polymer.

Ductility of the pressure sensitive polymer is not effected by vapor spraying with the polar agent, 1,1,1- trichloroethane, alone.

EXAMPLE 3 Following the procedure of Example 1, the ductility of the pressure sensitive polymer prepared according to Example 1, is increased by exposing the polymer to'a spray of dichlorofluoromethane, a dielectric polar agent.

EXAMPLE 4 Ductility of the pressure sensitive polymer of Example 1 is improved in the compression tests of Example 1 by exposure of the polymer to vapors of methanol, ethanol, and chloroform.

The process of the present invention is particularly advantageous in that it enhances the pressure fixability of the weakly crosslinked amorphous, pressure sensitive toners to a substrate when pressure is applied thereto. The reduced ductility of the pressure sensitive polymer achieved by the process of this invention, improves the capability of fixing toner images to support surfaces in shorter periods of time when pressure fixing is used either with or without the assistance of heat, when the pressure sensitive polymer is used in the toner composition.

EXAMPLE 5 Preparation of Toner The ionic polymer (19 parts) of Example 1, is dissolved in tetrahydrofuran (100 parts) and mixed with 1 part MOGUL L carbon black. The solvent is evaporated with stirring and final traces removed in a vacuum oven at C. The slab of ionic polymer is then ball milled in a polyethylene jar containing cylindrical stones for four hours and sieved through a 44 micron grid. The number average particle size is 9.0 microns.

EXAMPLE 6 An electrostatic latent image was developed with the toner composition described in Example 5. The developed image was then transferred in imagewise configuration to a receiving paper sheet which was then passed at room temperature between steel rollers adjusted to 400 pli (pounds per lineal inch) nip pressure, at a speed of four inches per second. Immediately thereafter the compressed toner image was sprayed for about three seconds with 250 mg. of a mixture of 1,1,1- trichloroethane and dichlorodifluoromethane.

The degree of fix was judged by noting the number of abrasion cycles in a standard abrasion tester to reach a predetermined level of image deterioration. The fixed image of this example was found to withstand more than five times as many abrasion cycles to reach the predetermined level of image deterioration than a control which was an image fixed by heat fusion.

This same procedure is repeated in every detail except that the toner image is sprayed prior to pressure rolling and simultaneously with pressure rolling. Results similar to those described in the above paragraph are obtained.

EXAMPLE 7 A hydrogen bonded polyamide (19 parts), the reaction product of dimer acids with linear diamines, commercially available from Emery Industries Inc., is mixed with 1 part MOGUL L carbon black in tetrahydrofuran lOO parts). The solvent is evaporated as de scribed in Example 5, and a toner is prepared by ball milling.

An electrostatic image is developed with the above toner composition. The developed image is transferred in imagewise configuration to a receiving paper sheet which is subjected to spraying for about 3 seconds with 250 mg. of n-propanol. The sheet is then passed at room temperature between steel rollers adjusted as in Example 6. Results similar to those of Example 6 are obtained where the fixed image withstands more abrasion cycles than a control treated only with pressure.

What is claimed is:

1. An improved process for fixing to a support surface a pressure sensitive electrostatographic toner of the type comprising a weakly crosslinked amorphous, pressure sensitive polymer having a glass transition temperature greater than about C, comprising exposing said toner to an agent which reduces the forces of associative bonding of said weakly crosslinked amorphous, pressure sensitive polymer, in conjunction with the application of pressure, to increase shear sensitivity of the polymer and thereby enhance pressure fixability at ambient temperatures.

2. The process of claim 1 wherein said agent comprises a vapor of a dielectric polar liquid.

3. The process of claim 1 wherein said agent comprises a dielectric polar liquid.

4. The process of claim 1 wherein said agent has a dielectric constant greater than about 3 at C.

5. The process of claim 3 wherein said dielectric polar liquid has a boiling point at atmospheric pressure of about 100C. or less.

6. The process of claim 3 wherein the dielectric polar liquid is water.

7. The process of claim 3 wherein the dielectric polar liquid comprises a low boiling halogenated hydrocarbon.

8. The process of claim 7 wherein the halogenated hydrocarbon is selected from the group consisting of chloroform, carbon tetrachloride, dichlorodifluoromethane and fluorodichloromethane.

9. The process of claim 7 wherein the dielectric polar liquid comprises an alcohol having from about 1 to 5 carbon atoms.

10. In an eleetrostatographic imaging method of the type comprising forming an electrostatographic latent image on a surface; developing the latent image with electroscopic marking materials of the type comprising a weakly crosslinked amorphous, pressure sensitive polymer having a glass transition temperature greater than about 20C, whereby pressure application to said weakly crosslinked, pressure sensitive polymer results in a polymer having the properties of the uncrosslinked polymer; transferring the developed image to a receiving substrate; and subjecting the developed image present on the substrate to pressure; the improvement comprising exposing said weakly crosslinked amorphous, pressure sensitive polymer to a dielectric polar agent which reduces the forces of associative bonding of said weakly crosslinked amorphous polymer, as well as subjecting the image present on the substrate to pressure, whereby shear sensitivity of the polymer is increased and the pressure fixability at ambient temperatures is enhanced.

l l. The method of claim 10 comprising applying said dielectric polar agent to said weakly crosslinked amorphous, pressure sensitive polymer in the exposure step, as a liquid.

12. The method of claim 10 comprising applying said dielectric polar agent to said weakly crosslinked amorphous, pressure sensitive polymer in the exposure step,

as a vapor.

13. The method of claim 10 wherein said dielectric polar agent comprises a liquid having a dielectric constant of greater than about 3 at 25C.

14. The method of claim 13 wherein said dielectric polar agent is water.

15. The method of claim 10 wherein said dielectric polar agent comprises a hydrocarbon havinga boiling point of about C. or less at atmospheric conditions.

16. The method of claim 10 wherein the dielectric polar agent comprises a low boiling halogenated hydrocarbon.

17. The method of claim 16 wherein the halogenated hydrocarbon is selected from the group consisting of chloroform, carbon tetrachloride, dichlorodifluoromethane and fluorodichloromethane.

18. The method of claim 10 wherein the dielectric polar agent comprises an alcohol having from about 1 to 5 carbon atoms.

19. The method of claim 10 wherein said weakly crosslinked amorphous polymer comprises styrene/nbutyl methacrylate/potassium methacrylate.

20. The method of claim 10 comprising exposing the weakly crosslinked amorphous, pressure sensitive polymer to the dielectric polar agent prior to subjecting the image to pressure.

21. The method of claim 10 comrising exposing the weakly crosslinked amorphous, pressure sensitive polymer to the dielectric polar agent simultaneously with subjecting the image to pressure.

22. The method of claim 10 comprising exposing the weakly crosslinked amorphous, pressure sensitive polymer to the dielectric polar agent following subjecting the image to pressure. 

1. AN IMPROVED PROCESS FOR FIXING TO A SUPPORT SURFACE A PRESSURE SENSITIVE ELECTROSTATOGRAPHIC TONER OF THE TYPE COMPRISING A WEAKLY CROSSLINKED AMORPHOUS, PRESSURE SENSITIVE POLYMER HAVING A GLASS TRANSITION TEMPERATURE GREATER THAN ABOUT -20*C, COMPRISING EXPOSING SAID TONER TO AN AGENT WHICH REDUCES THE FORCES OF ASSOCIATIVE BONDING OF SAID WEAKLY CROSSLINKED AMORPHOUS, PRESSURE SENSITIVE POLYMER, IN CONJUNCTION WITH THE APPLICATION OF PRESSURE, TO INCREASE SHEAR SENSITIVITY OF THE POLYMER AND THEREBY ENHANCE PRESSURE FIXABILITY AT AMBIENT TEMPERATURES.
 2. The process of claim 1 wherein said agent comprises a vapor of a dielectric polar liquid.
 3. The process of claim 1 wherein said agent comprises a dielectric polar liquid.
 4. The process of claim 1 wherein said agent has a dielectric constant greater than about 3 at 25*C.
 5. The process of claim 3 wherein said dielectric polar liquid has a boiling point at atmospheric pressure of about 100*C. or less.
 6. The process of claim 3 wherein the dielectric polar liquid is water.
 7. The process of claim 3 wherein the dielectric polar liquid comprises a low boiling halogenated hydrocarbon.
 8. The process of claim 7 wherein the halogenated hydrocarbon is selected from the group consisting of chloroform, carbon tetrachloride, dichlorodifluoromethane and fluorodichloromethane.
 9. The process of claim 7 wherein the dielectric polar liquid comprises an alcohol having from about 1 to 5 carbon atoms.
 10. In an electrostatographic imaging method of the type comprising forming an electrostatographic latent image on a surface; developing the latent image with electroscopic marking materials of the type comprising a weakly crosslinked amorphous, pressure sensitive polymer having a glass transition temperature greater than about -20*C, whereby pressure application to said weakly crosslinked, pressure sensitive polymer results in a polymer having the properties of the uncrosslinked polymer; transferring the developed image to a receiving substrate; and subjecting the developed image present on the substrate to pressure; the improvement comprising exposing said weakly crosslinked amorphous, pressure sensitive polymer to a dielectric polar agent which reduces the forces of associative bonding of said weakly crosslinked amorphous polymer, as well as subjecting the image present on the substrate to Pressure, whereby shear sensitivity of the polymer is increased and the pressure fixability at ambient temperatures is enhanced.
 11. The method of claim 10 comprising applying said dielectric polar agent to said weakly crosslinked amorphous, pressure sensitive polymer in the exposure step, as a liquid.
 12. The method of claim 10 comprising applying said dielectric polar agent to said weakly crosslinked amorphous, pressure sensitive polymer in the exposure step, as a vapor.
 13. The method of claim 10 wherein said dielectric polar agent comprises a liquid having a dielectric constant of greater than about 3 at 25*C.
 14. The method of claim 13 wherein said dielectric polar agent is water.
 15. The method of claim 10 wherein said dielectric polar agent comprises a hydrocarbon having a boiling point of about 100*C. or less at atmospheric conditions.
 16. The method of claim 10 wherein the dielectric polar agent comprises a low boiling halogenated hydrocarbon.
 17. The method of claim 16 wherein the halogenated hydrocarbon is selected from the group consisting of chloroform, carbon tetrachloride, dichlorodifluoromethane and fluorodichloromethane.
 18. The method of claim 10 wherein the dielectric polar agent comprises an alcohol having from about 1 to 5 carbon atoms.
 19. The method of claim 10 wherein said weakly crosslinked amorphous polymer comprises styrene/n-butyl methacrylate/potassium methacrylate.
 20. The method of claim 10 comprising exposing the weakly crosslinked amorphous, pressure sensitive polymer to the dielectric polar agent prior to subjecting the image to pressure.
 21. The method of claim 10 comrising exposing the weakly crosslinked amorphous, pressure sensitive polymer to the dielectric polar agent simultaneously with subjecting the image to pressure.
 22. The method of claim 10 comprising exposing the weakly crosslinked amorphous, pressure sensitive polymer to the dielectric polar agent following subjecting the image to pressure. 